Vannellidae tend to be flattened and fan-shaped during motion, although some are long and narrow, and have a prominent clear margin at the
anterior. In most amoebae, the
endoplasm glides forward through the center of the cell, but vannellids undergo a sort of rolling motion with the outer membrane sliding around like a
tank tread. These amoebae are usually 10-40 μm in size, but some are smaller or larger.
Vannellidae are surrounded by an outer covering called the
glycocalyx, which is generally 10-20 nm across, though the thickness varies among species. In some species, a layer of hair-like filaments called glycostyles protrudes from the glycocalyx. == Parasitism ==